By combining techniques in High Energy Physics (Multiwire Proportional Counter) with the state of the art in Digital Electronics (Mass Core Memory) we were able to set up a prototype of a computer controlled "Multireflection Diffractometer" for protein crystallography. The prototype system has been used to collect data from crystals of a complex of dihydrofolate reductase and methotrexate (a cancer drug). With this new system, one can collect data about thirty times faster than with the standard diffractometer (about 1400 reflection intensities per hour versus 50 reflection intensities per hour). The precision of the new data is also better with an intensity reliability R factor of 5 percent as compared with 6.7 percent from the diffractometer data. Continued financial support is solicited for a two-fold effort: a) to continue the technical development both in multiwire counter technique and in the data collection hardware and software culminating in a new system (MARK II) that can collect data efficiently of crystals of very large unit cells (up to 400 A); b) to use both the prototype and the new system to collect data to solve the high resolution structure of target enzymes of good cancer drugs. Our aim will be to understand the mechanism of action of these enzymes and to contribute to the rational development of new drugs of chemotherapeutic importance. BIBLIOGRAPHIC REFERENCES: A Xenon-filled Multiwire Area Detector for X-Ray Diffraction, C. Cork, R. Hamlin, W. Vernon, Nguyen-huu Xuong and V. Perez-Mendez, Acta. Cryst. 31, 702 (1975). Protein Data from the Multiwire Area Detector Diffractometer, Nguyen-huu Xuong, W. Vernon, C. Nielsen, R. Hamlin and C. Cork, A.C.A. program and abstracts, Vol. 5, No. 1, page 18 (1977).